Generally, there are MOS transistors having various types. Among various MOS transistors, an extended drain metal oxide semiconductor field effect transistor (hereinafter, referred to as “an extended drain MOS transistor”) having an extended drain region to enhance breakdown voltage (hereinafter, referred to as “BV”) of the transistor element has been developed. Particularly, such an extended drain MOS transistor has been widely used in high voltage applying conditions. First, a p-type well and an n-type drain region, which are separated from each other, are disposed on and/or over a semiconductor substrate having an active region restricted by an isolation layer. A source region is disposed on and/or over the p-type well. An upper portion of the p-type well, which is adjacent to the source region and is overlapped with a gate insulating film and a gate conductive film, is a channel region. The drain region is disposed on and/or over an extended drain region. The gate insulating film and the gate conductive film are sequentially stacked on and/or over the channel region, and a gate spacer film is formed on and/or over the side wall of the gate conductive film. A first ion implantation process is performed before formation of the gate spacer film and a second ion implantation process is performed after formation of the gate spacer film, and thus, a DMOS transistor structure is obtained through double diffusion. The source region and the drain region are electrically connected to source and drain electrodes respectively through general wiring.
As described above, in such an extended drain MOS transistor, the extended drain region is formed to prevent the destruction of the element at a high voltage. Here, the extended drain region increases the size of the element and generates leakage current between the source and drain regions.